Improved second-degree kinship analysis using the FGID forensic four-in-one DNA typing kit

In general, using additional genetic markers can greatly improve the system power and accuracy of complex kinship identification. In this study, we employed the FGID Forensic Four-in-one DNA typing kit on the DNBSEQ-G99RS platform to gather sequence information for 66 autosomal STRs (A-STRs) and 132 autosomal SNPs (A-SNPs) of 24 pairs of second-degree relatives (13 grandparent-grandchild pairs and 11 uncle/aunt-nephew/niece pairs) from 9 families, along with 100 unrelated Han Chinese individuals. The likelihood ratio (LR) and identical-by-state (IBS) methods were applied to the kinship analysis, respectively. As anticipated, compared to the results using the ForenSeq™ DNA Signature Prep Kit, the LR values for second-degree relatives improved with the addition of more STR and SNP markers in this study, while LR values for unrelated individuals decreased. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) all exceeded 0.9600 at the cut-off values of t₁ = -3 and t₂ = 3, with 96.80% of simulated relationship pairs accurately classified as either second-degree relationships or unrelated individuals. Furthermore, IBS values based on sequence-based STRs were significantly lower than those based on length-based STRs. Overall, these results indicated that the FGID kit, which incorporates an increasing number of genetic markers, could effectively enhance the system performance in second-degree kinship analysis.